1. Field of the Invention
The present invention relates to a transformer and, more particularly, to a low-profile transformer without a bobbin to reduced the volume.
2. Description of the Related Art
FIG. 9 shows a conventional transformer including a bobbin 1′, an iron core 2′, and primary and secondary windings 3′ and 4′. The bobbin 1′ includes a sleeve 11′ having a central through-hole 13′ through which the iron core 2′ extends. A groove 12′ surrounds the sleeve 11′ and receives the primary and secondary windings 3′ and 4′ spaced from each other by an insulating layer 14′. The primary and secondary windings 3′ and 4′ are enamel-covered wires. The iron core 2′ and the primary and secondary windings 3′ and 4′ create electromagnetic induction for voltage-changing purposes with the ratio of turns of the primary and secondary windings 3′ and 4′ being one of the factors. The bobbin 1′ and the primary and secondary windings 3′ and 4′ wound along an axis of the bobbin 1′ cause limitation to the reduction of the volume and height of the transformer, failing to provide a compact device. Furthermore, the sizes of the primary and secondary windings 3′ and 4′ are decided by the size of the bobbin 1′ around which they are mounted. Namely, it is difficult to create specifications for the primary and secondary windings 3′ and 4′ due to the winding shapes.
Taiwan Patent Publication No. 422-400 discloses a spiral coil 5′ for transformers. As illustrated in FIGS. 10 and 11, the coil 5′ includes an outer end 51′ extending from an outermost loop of the coil 5′. The other end 52′ of the coil 5′ extends from an innermost loop and across the loop portion of the coil 5′. Thus, more turns can be provided within a lower height A substantially equal to two times of the diameters of the wire. However, there is still a waste of space (see the section indicated by B).
Thus, a need exists for a low-profile transformer with a reduced volume without using a bobbin.